The invention relates to an alternating current electrical transformer and more particularly to a toroidal electrical transformer having a core wound from one or more continuous strips of core material and high and low voltage windings, each wound in substantial part from a continuous conductor.
Ideally, an electrical toroidal transformer having a continuously-wound, annular or toroidal core and continuous toroidal low voltage and high voltage windings, with each winding or segment thereof being wedge-shaped, would provide a transformer of nearly optimum operating efficiency. The continuously wound annular or toroidal transformer core of such a transformer would minimize the effective magnetic path length and the parasitic core losses. Furthermore, the continuous toroidal electrical windings of such a transformer with each winding being wedge-shaped, would optimize the use of an annular or toroidal transformer core by providing the smallest effective electrical coil path length. Previously known transformer designs have not, however, accomplished all of these objectives.
Various proposals have been made to provide a transformer having a wound, annular core and toroidal windings surrounding the core. For example, the patent to Bastis, et al, U.S. Pat. No. 3,430,489, issued Sept. 5, 1967, discloses an air-cooled toroidal transformer in which the core is severed into two segments so that the windings can be positioned onto the core segments before they are joined. A similar technique is shown in the patent to Conner, et al, U.S. Pat. No. 3,996,543, issued Dec. 7, 1976. A segmented core is used in Conner, et al, because of the problems associated with winding the primary and secondary windings on a continuous toroidal core using conventional winding machines.
Efforts have been made to wind a more-or-less continuous annular or toroidal core into preformed, generally-rectangular primary and secondary windings. Examples of such efforts are shown in the patents to Humphreys, U.S. Pat. No. 2,191,393, issued Feb. 2, 1940; Vance, U.S. Pat. No. 2,249,506, issued July 25, 1941; Granfield, U.S. Pat. No. 2,160,588, issued May 30, 1939; Boyajian, U.S. Pat. No. 2,245,180, issued June 10, 1941; Brand, U.S. Pat. No. 2,246,239, issued June 17, 1941; Brand, U.S. Pat. No. 2,246,240, issued June 17, 1941; Camilli, U.S. Pat. No. 2,248,606, issued July 8, 1947; Driftmeyer, U.S. Pat. No. 2,282,854, issued May 12, 1942; Steinmayer, U.S. Pat. No. 2,344,006, issued Mar. 14, 1944; and Steinmayer, U.S. Pat. No. 2,401,984, issued June 11, 1946. The aforementioned patents, however, illustrate that it was not deemed feasible to wind such a continuous core into continuous, preformed toroidal windings.
Finally, a process for heat treating a toroid wound from an amorphous metal material is disclosed in a patent issued to Becker et al, U.S. Pat. No. 4,116,728, issued Sept. 26, 1978; and a process for dipping a pre-formed electrical coil in a liquid insulation bath and curing the insulative coating in an oven is disclosed in a patent issued to Schou, U.S. Pat. No. 2,061,388, issued Nov. 17, 1936. According to the present invention, a toroidal electrical transformer of near optimum efficiency includes a wound magnetic core that is continuous at least in substantial part and generally toroidal or annular in configuration. The magnetic core is surrounded by high and low voltage coils or windings that are also continuous in substantial part and generally toroidal in configuration. Such high and low voltage coils or windings form an arcuate elongated passage extending therethrough in which the magnetic core is disposed. Although the arcuate elongated passage encompasses at least one-half of the circumferential length of the magnetic core, the advantages of the present invention are best obtained if such arcuate elongated passage encompasses 75 to 95 percent of said circumferential length of the magnetic core.
The above structure and configuration is preferably accomplished by preforming the high and low voltage windings into two coreless and semi-toroidal or arcuate transformer portions or sections, each constituting substantially one-half of the transformer. The magnetic core material is then fed through a small circumferentially-extending gap between adjacent ends of such semi-toroidal portions or sections and continuously wound in place into the generally toroidal or arcuate elongated passage formed in said portions or sections. Such circumferentially-extending gap is preferably sufficient in circumferential length, but not longer than necessary, to allow the magnetic core material to be fed therethrough and wound in place within the arcuate elongated passage to form the annular magnetic core.
In the preferred embodiment of the toroidal transformer, the high voltage coil or winding is wound into a number of wedge-shaped bundles or segments with connecting loops of wire or conductor. Preferably in order to achieve the advantages of the invention, such wedge-shaped segments and connecting loops are wound and formed from a pre-insulated wire or conductor that is continuous over 30 to 50 percent of the total length of the high voltage coil. At a minimum, according to the invention, each wedge-shaped segment is wound and formed from a continuous wire or conductor.
The low voltage coil or winding in the preferred embodiment is wound and formed from conductor stock in a singular or a multifilar arrangement wherein each turn is wedge-shaped and may also be composed of two parallel coils interleaved in a spiral or double helix configuration as is explained in detail below. Preferably in order to achieve the advantages of the invention, such conductor is continuous over 30 to 50 percent of the total length of the low voltage coil for at least each voltage winding thereof in a multi-voltage arrangement. At a minimum, according to the invention, such low voltage conductor is continuous over three or more turns of the coil in each of the above-mentioned transformer portions or sections for each voltage winding thereof.
The preferred magnetic core is fed through a gap between the ends of the high voltage and low voltage windings and is wound in place into a generally toroidal or annular opening which extends through the high and low voltage coils to form an arcuate elongated passage therethrough. The core is preferably formed and wound from a single continuous ribbon-like strip of core material. Alternatively, however, the magnetic core may be wound from a number of continuous strips of core material in a parallel bifilar or parallel multifilar arrangement. Also, in the construction of very large toroidal transformers, a separate single strip or a multifilar group of strips may be used to wind an inner portion of the core diameter, with one or more subsequent single strips or multifilar group of strips serially connected thereto for forming increasing diametric regions or portions of the wound core. In this configuration, the subsequent, or serially-connected, single strips or groups of strips may include different types of core material, having different loss characteristics, at different diametric regions of the wound core as is described in U.S. Pat. No. 4,025,288, issued to Lin et al, on May 27, 1980. In such serially wound configurations, the magnetic core is considered to be substantially continuous or continuous in substantial part.
The toroidal or arcuate configuration of the high and low voltage coils in the preferred embodiment is that of a torus generated by the revolution of a generally trapezoidal shape about an external axis, while the toroidal or annular configuration of the preferred magnetic core is that generated by the revolution of a generally rectangular shape about an external axis with such core configuration being substantially defined by the above-mentioned arcuate elongated passage through the high and low voltage coils. As is explained below, however, such toroidal configurations may alternatively be those generated by the toroidal revolution of any of a number of geometric shapes, including, for example, circles, ovals, squares, or even irregular shapes.
Since the core structure in the present invention is continuous, as described above, magnetic flux losses due to gaps or breaks in the core material are minimized. Since the structure of the primary and secondary windings is continuous in substantial part, as described above, electrical losses due to connections in those windings are likewise minimized. Because the high voltage and low voltage windings are toroidal in configuration, with each winding segment being wedge-shaped, optimum use is made of the wound-in toroidal or annular transformer core. The minimizing of such magnetic flux losses and electrical losses is especially timely since energy conservation is presently a national goal.
A toroidal electrical transformer according to the invention is preferably constructed by preforming the high voltage and low voltage coils or windings, which are then assembled onto toroidal or annular insulation structures to form a coreless toroidal winding and insulation structure having a generally annular or toroidal-shaped central void or core-forming tunnel which forms an arcuate elongated passage therethrough. Thereafter, the core material is fed into the preformed toroidal winding and insulation structure through a relatively small, circumferentially-extending gap between adjacent ends of the portions or sections of such structure and wound in place to form the finished transformer. Various novel techniques are disclosed herein to accomplish these steps.
Of particular importance is the fact that the core material of a toroidal transformer according to the invention may be extremely thin. Recent advances in core material technology have provided amorphous metals, an example of which is known by the tradename METGLAS. Because such amorphous metals are fabricated by solidifying the molten metal in a very short period of time, such amorphous metals must be of an extremely thin gauge as compared with core materials composed of conventional grain-oriented metals. Such thin-gauge core materials are difficult, if not impractical, to use with conventional core manufacturing techniques. The transformer manufacturing method of the present invention, however, can efficiently accommodate such thin-gauge amorphous metal core materials, thereby further improving the efficiency and reducing the parasitic losses of the transformer.
Other features and advantages of the invention will become apparent in the description of the preferred embodiments set forth below.